Hi,
If you have lost your cert, contact the centre where you appeared in the test, if they give you a new one then OK, otherwise you may have to appear in test again, as this thing is very clearly mentioned in instruction that if you loose your certificate you have to appear in test again.
I will strongly suggest you don't send any photocopies to Home Office and don't take any chances with your application, as if you will give them a chance to refuse your application by providing a photo copy, and if your application is refused means you have to go for appeal and you will waste loads of money and valuable time so just spend 35£s and bit of hardwork again.
Rest upto you
Kind regards
Seenan